High-powered optical sources have many applications in which an intense beam of light is focused onto a substrate or other target. Many high power optical systems make use of wavelength conversion to produce light having a desired wavelength or range of wavelengths. Often the process of conversion involves performing some non-linear optical wavelength conversion on input light from a source, such as a laser. The wavelengths that can be produced by nonlinear optical wavelength conversion are limited however by the wavelengths that can be produced with available lasers and the nonlinear optical wavelength conversion processes. For example, many wavelength converted laser systems are based on a seed laser that produces light at a fundamental vacuum wavelength of 1064 nanometers. The infrared 1064 nm light can be converted to 532 nm visible light by nonlinear frequency doubling.
It would be desirable to have a light source that can produce light at new wavelengths that cannot be reached by the usual nonlinear conversion processes for 1064 nm laser light. It would also be desirable to be able to easily select from among several different wavelengths of available laser light. An example of an application of such a light source is super-resolution microscopy, such as Stimulated Emission Depletion (STED) microscopy. The STED technique operates on a sample that has been tagged with a fluorescent dye, and uses a depletion laser to de-excite the dye molecules except in a very small region. The source of subsequent fluorescence can then be located to within tens of nanometers. The highest resolution is achieved when the depletion laser is pulsed rather than continuous.
It is within this context that embodiments of the present invention arise.